Xplained

By Suzanne D. Vernon, PhD, Scientific Director

The announcement on October 8, 2009, that an infectious retrovirus called XMRV (xenotropic murine-related retrovirus) was linked to CFS, could be the game-changing scientific event we have been waiting for. Whether XMRV provides the long-awaited causal link will depend on the findings described in the Science paper being replicated by another laboratory in another group of CFS patients. To help clarify what we know, let’s review the findings.

Dr. Judy Mikovits and her team at the Whittemore Peterson Institute for Neuro-immune Disorders (WPI) made a very insightful connection three years ago. XMRV was first described in prostate cancer in 2007 by investigators at the Cleveland Clinic, who also reported that XMRV-positive prostate cancer patients have alterations in RNase L, an antiviral immune system pathway. The WPI investigators knew that RNase L activity is also altered in blood cells from CFS patients and they made the decision to look for XMRV in CFS patients with this immune defect.

When scientists want to find a virus, we look for it in the sickest individuals because often this is where there is likely to be the highest levels of a virus, if present. Dr. Dan Peterson has been caring for and researching CFS patients since the 1984 Incline Village outbreak, so he identified CFS patients with prolonged disabling fatigue, cognitive impairment, and documented laboratory immunological abnormalities (including altered RNase L activity) to hunt for XMRV.

The WPI laboratory team detected XMRV sequences in 68 of 101 (67%) CFS patients tested and in 8 of 218 (3.7%) healthy control subjects. The Cleveland Clinic confirmed the presence of XMRV in a subset of these same CFS cases, 7 of the 11 (64%) samples from WPI. The Cleveland Clinic researchers found that the CFS XMRV was similar to prostate cancer XMRV, and not a mouse virus (murine leukemia virus) that could have been a contaminant explaining the discovery.

The investigators designed several laboratory tests to understand XMRV. They looked to see if XMRV was expressed in peripheral blood mononuclear cells (PBMCs) of CFS patients. PBMCs circulate throughout the entire system and can be important “sentinels” for processes occuring in the body. PBMCs from 19 of 30 CFS patients expressed XMRV proteins compared to 0 of 16 PBMC samples from healthy controls. They also wanted to know which cells harbored XMRV; they found it in T and B cells in the blood of one CFS patient. The investigators looked to see if the XMRV from CFS patients was infectious. Both blood cells and plasma (the cell-free fraction of blood) from XMRV-positive CFS patients were able to transmit this virus to a susceptible cell line, indicating infectiousness in laboratory culture. Finally, they wanted to know if XMRV stimulated the immune system to produce antibodies. Plasma from 9 of 18 CFS patients had antibodies that reacted with a virus protein similar to that found in XMRV, compared to no reaction from plasma of 7 healthy controls.

This Science paper tells us that XMRV plays a possible role in CFS pathogenesis in these CFS patients. How much we can generalize these findings to other CFS patient populations? That answer will depend on the results of replication studies.

The design of replication studies should include CFS patients who are similar to those reported in the Science study. Dr. Peterson reported at the Oct. 29 CFS Advisory Committee meeting that the 101 patients in the study were drawn from CFS practitioners in Nev., Calif., Ore., Fla., N.C., and N.Y. They ranged in age from 19 to 75 with a mean age of 55. Sixty-seven percent were female. The controls were age, sex and zip-code matched and were not contacts of the patients studied, nor were they lab workers.

Methods used in independent replication studies should also follow the WPI protocol and use similar reagents. We are actively working with several independent research groups in the U.S. and other countries to expedite these studies.

While these exciting studies of XMRV continue, the Solve ME/CFS Initiative continues its support of our funded investigators. It’s important to remember that HIV was discovered to be the cause of AIDS 26 years ago, but worldwide research on AIDS treatment, cure and prevention continues today. Our funded investigators’ research on why Epstein-Barr triggers CFS, whether ion-channel receptors are markers of fatigue, why CFS patients have higher rates of leaky gut, why CFS patients have slow blood flow to the brain, why CFS patients have metabolic disturbances in the brain, and how we can bring this information, as well as XMRV, together using powerful computational tools are all important as we work together to solve CFS.